Thin-Air ATSC: Various Data Bits For Thee
This blog post references my cover story ‘Thin-Air ATSC: Reception Isn’t Always Easy‘ in EDN’s May 14, 2009 edition. It’s one of a series of web addendums to the print writeup.
Although my OTA (over-the-air) digital television reception situation is somewhat stable at this point (and yes, I realize I’ve just jinxed myself by typing that), I’m still struggling with the Reno, NV CBS affiliate, KTVN. Sometimes, I’m able to reliably tune in the signal coming from the station’s primary transmitter on Slide Mountain, although Windows Media Center reports that the received beacon is somewhat weak. But other times of day (and on only some days…the degradation isn’t day-to-day repeatable), KTVN’s signal disappears. An email I received last Thursday from EDN reader and cable TV consultant Paul Williams clued me in to a possible reason for this seemingly random reception-or-not phenomenon.
Paul brought up the topic of temperature inversion. His comments were specific to coastal regions, but the issue also affects regions like mine which experience wide temperature swings across any 24-hour time period, coupled with Reno’s high desert landscape. Within the troposphere (lower atmosphere) the ambient temperature normally increases as distance to the ground decreases, but a variety of phenomenon can sometimes reverse this trend. When temperature inversion is active, RF signals that would normally travel out into space are instead refracted back towards the ground (a phenomenon called tropospheric propagation), enabling reception hundreds and even thousands of miles away from the source antenna.
According to Paul, however, coastal temperature inversions (beginning at ‘prime time’ viewing hours in the evening, and continuing through mid-morning the next day) can also degrade deep fringe reception. I’m not quite sure why this occurs, and Paul hasn’t yet responded to my email inquiry, so I’d appreciate feedback from other readers. More generally, though, if VHF and UHF signal paths are affected both by ambient temperature and the temperature gradient with altitude, this phenomenon could explain my varying reception of KTVN. If you revisit the TVFool analysis results I first shared with you in early August of last year (which, note, only lists primary transmitters, not translators):
You’ll see that, as last Thursday’s cover story points out, KTVN’s signal gets double knife-edge diffracted (presumably over both the summit of Slide Mountain and the crest of the Mount Rose Range) prior to reaching me. Even a slight alteration of this dual diffraction path could mean the difference between reception success and failure, especially when you consider that:
- Even under optimum conditions, TVFool estimates (for unknown reasons) that KTVN’s received signal at my location is more than 5 dB lower than that of its next-door broadcast antenna neighbor, KRNV, the Reno NBC affiliate which I’m consistently able to tune in as long as I use the Antennas Direct CPA-19 signal booster, and
- Past testing showed that my home’s internal coax wiring particularly attenuates VHF channel 13, used by KTVN.
I’m going to try tuning in KTVN’s translator for Verdi, NV on Peavine Peak, instead of the primary signal on Slide Mountain, to see if I get more consistent reception that way. Paul also recommended that I try Kitz Technologies’ Model KT-100VG Antenna Booster, with which his clients have had great success.
With less than one month to go before the rescheduled phase-out of full power NTSC transmissions across the United States, I’m not hearing any serious rumblings of further push-outs. Perhaps this is because, as Engadget recently reported, Nielsen now estimates DTV un-readiness at less than 3% of the potentially affected population. And as you’ll see in the video clip below, many stations are delighted to be able to shut off their ancient and expensive-to-operate analog TV broadcast equipment:
However, as I noted in the ‘A San Francisco Bay Area Equivalence‘ sidebar to the main article, some folks may still wake up to an unpleasant surprise the first time they try to tune in ATSC, due to ‘cliff effect’ reception issues caused by geographic attenuation (natural or human-made). As such, and as my article suggested might happen, the U.S. Senate is currently considering a bill that would allocate funds for the purchase and installation of additional terrestrial repeaters and translators.
My cover story, along with a prior blog post, suggested that a netbook might serve (among other things) as a compelling ATSC portable television. I was therefore intrigued to recently hear that Dell is reportedly planning on offering a branded ATSC antenna-and-receiver accessory for its Mini 10 netbook. And for PC manufacturers that might want to bundle OTA digital television capability from the get-go, Intel’s developing an embedded antenna design.
White Spaces technology backers, along with Qualcomm’s MediaFLO group and FCC spectrum auction winners such as AT&T and Verizon, are hungrily awaiting the vacancy of frequency bands currently in use by NTSC transmitters. As such, I thought you might be interested in perusing some recent White Spaces coverage that I’ve archived:
- Find out where TV’s ‘white spaces’ are, online
- TV Broadcasters Attempt to Block White Space Use
- White spacers press FCC on database plan
- IEEE begins work on wireless standards for white spaces access
- Internet Hardware For White-Space Spectrum?
- Google Urges National Inventory of Radio Spectrum
And finally, elaborating on the heavy snowfall historical data at my home office location that I shared in my cover story, enjoy the following links 
Brian Dipert commented:
